The present invention relates in general to vehicle wheels and in particular to a plated vehicle wheels.
Vehicle wheels include an annular wheel rim which is adapted to carry a pneumatic vehicle tire. The ends of the wheel rim include annular recesses which form a pair of tire bead seats. When a tire is mounted on the wheel rim, the tire bead seats support tire beads which are formed on the inside edge of the walls of the tires. An air-tight seal is formed between the tire bead seats and the tire beads to retain inflation air within the tire.
Vehicle wheels also include a circular wheel disc which can be formed across the outboard end of the wheel rim or recessed within the wheel rim. The wheel disc includes a wheel hub having a central pilot hole and a plurality of wheel stud holes formed therethrough for mounting the wheel upon a vehicle. Typically, the wheel disc also includes a plurality of wheel spokes connecting the wheel hub to the rim.
In the past, vehicle wheels have usually been fabricated by attaching a stamped steel disc to a rolled steel rim. Vehicle wheels also have been cast or forged from steel billets. Increasingly, however, vehicle wheels are being formed from light weight metals, such as aluminum, magnesium, titanium, or alloys thereof. Such light weight metal wheels can be cast or forged as a one-piece wheel or assembled by attaching a full or partial wheel disc to a wheel rim. A wheel assembled from a wheel disc and rim formed from dissimilar metals is referred to as a bimetal wheel. For example, a cast aluminum alloy full face wheel disc, which includes the outboard tire bead seat, can be welded indirectly to a partial rolled steel wheel rim. A weld anchor formed from a ferrous metal is usually included in the wheel disc to facilitate forming the weld between the wheel disc and the wheel rim. Additionally, wheels can be formed from plastic.
With all wheels, regardless of the material used to form the wheel, the outer surface of the wheel disc is visible when the wheel is mounted upon a car. Accordingly, the wheel disc can be formed having a pleasing aesthetic shape. The wheel disc outer surface may be machined to form a smooth surface. Frequently a surface finish which typically has a decorative high luster is applied to the surface of the wheel disc or the entire wheel.
One type of surface finish, which is used extensively, is formed by chrome plating the surface of the wheel. During chrome plating, a layer of chromium, which can be polished to a high luster, is deposited upon the surface of the wheel. Known methods for forming a layer of chromium on a wheel surface are complex and typically require a number of discrete steps involving chemical deposition of multiple layers of metal onto the wheel surface.
A typical chrome plating process includes preparing the wheel by immersion in a solvent bath. The solvent bath removes oils and dirt from the wheel surface. The oils and dirt could inhibit adhesion of metal deposits to the wheel surface. The wheel also is prepared by immersion in a chemical bath to dissolve any surface oxides. This further improves the adhesion of metal deposits to the wheel surface. The wheel is then rinsed by immersion in a water bath or spraying with a high pressure water jet. The preparatory steps of removing oil and dirt, dissolving surface oxides and flushing are typically referred to as cleaning the wheel surface.
After cleaning, the chrome plating process begins with the total immersion of the wheel in a chemical bath containing a solution of nickel. During immersion, a thin first layer of nickel is chemically deposited upon the wheel surface to enhance adhesion of successive metal layers thereto. This first nickel layer tends to have a relatively uneven surface. Accordingly, a copper layer is chemically deposited over the first nickel layer, usually by immersion of the wheel in another chemical bath which contains copper in solution. The copper layer fills in uneven portions of the first nickel layer, forming a smooth surface. To further enhance the surface smoothness, the copper layer can be buffed. A second nickel layer, often referred to as a semibright nickel layer is chemically deposited over the buffed copper layer. The semibright nickel layer provides corrosion resistance. Next, a layer of nickel containing sulfur is chemically deposited over the semibright nickel layer as a sacrificial corrosion layer. A final bright nickel layer is chemically deposited onto the wheel surface to provide reflectivity and brightness to the wheel surface.
The chrome plating process continues with the deposit of multiple chromium layers over the nickel and copper layers. A first chromium layer is chemically deposited over the bright nickel layer. This layer is usually formed from discontinuous chrome, or pixy dust, to provide a more durable surface layer. A second layer of chromium is chemically deposited over the first chromium layer to prevent nickel fogging.
During the chrome plating process, each successive metal layer is typically deposited onto the wheel surface during total immersion of the wheel in a chemical bath containing a solution of the particular metal. Thus, the entire surface of the wheel, including the surfaces of the tire bead seats, is plated. Each successive metal layer is chemically bonded to the preceding layer to provide a durable and attractive decorative surface coating on the wheel. Furthermore, the wheel and the chemical bath are usually electrically charged with opposite polarities to accelerate the plating process. When this is done, the metal layers are electro-deposited onto the wheel surface.